Theoretical Electrotechnics


Students should become able to apply the laws of electromagnetism to derive from them the properties of phenomena relevant to Electrotechnics, and the grounds of real equipment’s technical behaviour. They must learn the functioning, properties, and general behavior of electrical circuits operating in AC regime (including power factor issues and 3-phase circuits) and of transformers (including some dimensioning aspects related to efficiency).  The transmission lines operation principle and related models will also be presented for students acquire the necessary basic knowledge to understand electrical energy transmission issues. 

General characterization





Responsible teacher

Anabela Monteiro Gonçalves Pronto


Weekly - 5

Total - 72

Teaching language



Students should have solid knowledge about eletcromagnetism nd mathematics in order to facilitate the comprehension of Electrotechnics topics.


  1. C. Alexander and M. Sadiku, Fundamentals of Electric Circuits, Mc-Graw Hill, 2nd Ed., 2002 
  2. Bessonov, L., Electricidade Aplicada para Engenheiros, Livraria Lopes da Silva, 1977
  3. Joseph A. Edminister, Circuitos Elétricos, Schaum MCGraw-Hill d0 Brasil, 2nd ed., 1985
  4. A.E. Fitzgerald, Charles Kingsley, Jr., Stephen D. Umans, Electric Machinery, 6th ed., McGraw-Hill, 2003. ISBN 0-07-366009-4
  5. Anabela Pronto, Slides of theoreticl classes, FCT NOVA, 2020.
  6. Ventim Neves, Apontamentos de Eletrotecnia Teórica (teóricas e práticas), FCT/UNL, 2000

Teaching method

Scientific principles are explained by professor at theoretical classes, supported by slides presentation. Students oral communication are stimulated through debate around technical and scientific questions. In practical classes two situations occur: in some classes, a group of technical problems are presented to be solved by students based on theoretical classes, in other students make laboratory work about specific parts of the subject in order to get some contact and experience with electrical installations and transformers, for example. In both cases, the debate between students is promoted and a qualitative evaluation is taken into consideration.


Written tests will be made structured in a way that students show if they are able to apply the knowledge acquire during theoretical and practical classes.

The students must present written reports describing laboratory work and, specially, analyzing and discussing the obtained results. In this component of evaluation process, teachers also want to promote team work skills and oral and written communication skills.

Both evaluation components will be tken into consideration to the finl mark, and in both components the student should hve a positive evluation (>= 10, in a 0 to 20 scale).

Evaluation method

The evaluation method could be one of the following:

 a) 2 Minitestes (MT) + 2 Labortory Work (TL) 

Mark (MT) = (0,40*MT1+0,60*MT2) >= 9,5 val.  

Mark(TL) = (0,50*TL1+0,50*TL2) >= 9,5 val. where TL1 >= 8,0 val.  and  TL2 >= 10,0 val.

Final Mark = 0,75*Mark(MT) + 0,25*Mark(TL) >= 9,5 val.

b) Final Exam (Ex) +  2 Labortory Work (TL) 

 Final Ex. Mark  >= 9,5 val. 

 Mark (TL) = (0,50*TL1+0,50*TL2) >= 9,5 val. where TL1 >= 8,0 val.  and  TL2 >= 10,0 val.

Final Mark = 0,75*Mark(MT) + 0,25*Mark(TL) >= 9,5 val.

In either case, the student will be approved if, and only if, his/her grade is equal to or higher than 9.5 (scale 0 to 20)"

If teachers considered so, any of the evaluation elements could be subjected to oral discussion.

Students with practical component already concluded and approved in previous years will be dismmed of doing it again, if they wish. In any case, students must inform the teacher about their decision: if they want to keep the previous mark or to repeat the laboratory component.

Subject matter

• Sinusoidal regimen. Complex notation. Circuits. Impedance. Vector diagrams. Geometric places with variation of parameters. Power.

• Three phase regimen. Balanced and unbalanced three phase systems. Line quantities and 

line-to-line quantities. Powers. Symmetrical Components.

• Magnetostatics: Ampère’s law. Magnetic circuits. Induction Flux. Coils. Linked flux, induction coefficients, magnetic linkage coefficient. Leakage and leakage induction coefficients. Ferromagnetism. Saturation and Hysteresis. Iron yoke coil.
• Transformer. Composition and equations. Real, perfect and ideal transformers. Leakage induction coefficients. Magnetizing current and iron losses. Reduction to the primary.  Steinmetz’ equivalent circuit. Sinusoidal regimen. Short circuit and open circuit. Tests. Vectorial diagrams. Voltage drop and voltage regulation.
• Electromagnetic fields. Maxwell’s equations. Plane wave solution. Propagation of pulses. Complex notation of vectors. Waves in sinusoidal regimen. Conditions at the borders, Incident and Reflected waves.

• Fields in conducting media. Effect. Rectangular embedded conducting bar and cylindrical conductor cases.
• Transmission Line: Distributed parameters. Propagation of pulses in lossless lines.Sinusoidal Regimen: ondulatory parameters. Standing wave. Reference to Smith’s chart. Input impedance. Line’s equivalent circuits. Short Lines.
• Rotating machine with non-salient poles and distributes winding. Magnetic field distribution in the air gap. Pulsing field. Triphase winding. Rotating field. Machines’ monophase and triphase induction coefficients. Monophase equivalent for triphase regimen.


Programs where the course is taught: